Yuya Hu

Abstract

An efficient biocatalytic approach for enantio‐ and regioselective ring‐opening of styrene oxides with cyanate was developed by using the halohydrin dehalogenase HheC from Agrobacterium radiobacter AD1, generating the corresponding chiral 5‐aryl‐2‐oxazolidinones in up to 47% yield and 90% ee. Additionally, the origin of enantioselectivity and regioselectivity of the HheC‐catalyzed cyanate‐mediated ring‐opening process was uncovered by single enantiomer bioconversions and molecular docking study.

Synlett
DOI: 10.1055/s-0039-1691405

Cheap and readily available 2-aminopyridine and related compounds can be used as organocatalysts for the conversion of epoxides into cyclic carbonates. This reaction gives high conversions under solvent-free conditions and is amenable to a kilogram-scale conversion under mild conditions.
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© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
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Abstract

An efficient deuteration process of α‐C−H bonds in various carbonyl‐based pharmaceutical compounds has been developed. Catalytic reactions are initiated by the action of Lewis acidic B(C₆F₅)₃ and D₂O, converting a drug molecule into the corresponding boron‐enolate. Ensuing deuteration of the enolate by in situ‐generated D₂O⁺−H then results in the formation of α‐deuterated bioactive carbonyl compounds with up to >98% deuterium incorporation.

Tune the pincer: A solid‐phase synthesis approach is described to prepare a diverse library of nonsymmetrical PNP pincer ligands. The heterogenized library is applied in ruthenium‐catalyzed hydrogenation of esters and lactones under mild conditions. Catalyst recovery and recyclability are facilitated by covalent attachment to solid supports.

Abstract

In contrast to their symmetrical analogues, nonsymmetrical PNP‐type ligand motifs have been less investigated despite the modular pincer structure. However, the introduction of mixed phosphorus donor moieties provides access to a larger variety of PNP ligands. Herein, a facile solid‐phase synthesis approach towards a diverse PNP‐pincer ligand library of 14 members is reported. Contrary to often challenging workup procedures in solution‐phase, only simple workup steps are required. The corresponding supported ruthenium‐PNP catalysts are screened in ester hydrogenation. Usually, industrially applied heterogeneous catalysts require harsh conditions in this reaction (250–350 °C at 100–200 bar) often leading to reduced selectivities. Heterogenized reusable Ru‐PNP catalysts are capable of reducing esters and lactones selectively under mild conditions.

Getting a hold of unfunctionalized alkenes: Optimization of the ligand in the iridium catalyst enables the asymmetric hydrogenation (AH) of unfunctionalized tetrasubstituted acyclic olefins, which installs two vicinal stereocenters with excellent stereoselectivies.

Abstract

Asymmetric hydrogenation has evolved as one of the most powerful tools to construct stereocenters. However, the asymmetric hydrogenation of unfunctionalized tetrasubstituted acyclic olefins remains the pinnacle of asymmetric synthesis and an unsolved challenge. We report herein the discovery of an iridium catalyst for the first, generally applicable, highly enantio‐ and diastereoselective hydrogenation of such olefins and the mechanistic insights of the reaction. The power of this chemistry is demonstrated by the successful hydrogenation of a wide variety of electronically and sterically diverse olefins in excellent yield and high enantio‐ and diastereoselectivity.

In this work, the carbon‐carbon double bond of unsaturated carbonyl compounds is readily reduced by a phosphetane oxide catalyst in the presence of a simple organosilane as terminal reductant and water as the hydrogen source. A catalyst screening was conducted and quantitative hydrogenation was observed when 1.0 mol% of a methyl substituted phosphetane oxides was employed as the catalyst. The procedure is highly selective towards activated double bonds tolerating a variety of functional groups which are usually prone to reduction. In total, 25 alkenes and two alkynes were hydrogenated to the corresponding alkanes in excellent yields up to 99%. Notably, less active poly(methylhydrosiloxane) could also be utilized as the terminal reductant. Mechanistic investigation revealed the phosphane as the catalyst resting state and a protonation/deprotonation sequence as the crucial step in the catalytic cycle.

Publication date: Available online 28 November 2019

Source: Chem

Author(s): Jorge Gascon

News on NP₃ ring systems: The reactivity of chlorinated NP₃ ring systems was investigated by experimental and computational methods. Comparisons with known N₂P₂ and P₄ congeners are drawn to obtain a systematic understanding of the reactivity of these types of compounds.

Abstract

The reactivity of the four‐membered NP₃ ring system [RN(μ‐PCl)₂PR] (R=Mes*=2,4,6‐tri‐tert‐butylphenyl) towards Lewis acids, Lewis bases, and reducing agents was investigated. Comparisons with the literature‐known, analogous cyclic compounds [ClP(μ‐NR)]₂ (R=Ter=2,6‐dimesitylphenyl) and [ClP(μ‐PR)]₂ (R=Mes*) are drawn, to obtain a better systematic understanding of the reactivity of cyclic NP species. Apart from experimental results, DFT computations are discussed to further the insight into bonding and electronic structure of these compounds.

Poly put the CO₂ on! The present review aims to report the updates and challenges in CO₂‐based (poly)carbonate synthesis. It focuses on progress realized in the preparation of cyclic carbonate synthons and aliphatic polycarbonate preparation from CO₂/epoxide copolymerization. Furthermore, all metal‐based processes are comprehensively discussed and the rapidly developing field of organocatalytic approaches is included.

Abstract

The utilization of carbon dioxide as a comonomer to produce polycarbonates has attracted a great deal of attention from both industrial and academic communities because it promises to replace petroleum‐derived plastics and supports a sustainable environment. Significant progress in the copolymerization of cyclic ethers (e.g., epoxide, oxetane) and carbon dioxide has been made in recent decades, owing to the rapid development of catalysts. In this Review, the focus is to summarize and discuss recent advances in the development of homogeneous catalysts, including metal‐ and organo‐based complexes, as well as the preparation of carbon dioxide‐based block copolymer and functional polycarbonates.

A valuable and operationally simple experimental approach to prepare perfluoroalkylated β‐fluoroenones and related compounds is described, providing a general approach to a variety of synthetically useful perfluoroalkylated β‐fluoroenones in moderate to high yields and excellent stereoselectivities.

The synthesis of fluorinated compounds is of increasing importance for the preparation of new pharmaceuticals and agrochemicals. For this purpose, the development of general and selective synthetic methods, which allow the preparation of versatile and scalable building blocks, is required. In this respect, here we report a facile and practical method for the stereoselective synthesis of fluoroalkylated β‐fluoroenones from ubiquitous ketones. The presented transition‐metal‐free procedure makes use of an amine promoter and easily available starting materials. It features broad substrate diversity with excellent stereoselectivity. In general, this novel strategy provides a facile synthesis of structurally diverse (per)fluoroalkylated β‐fluoroenones, which can be further transformed to various potentially bioactive molecules in a straightforward manner.

Abstract

An efficient deuteration process of α‐C−H bonds in various carbonyl‐based pharmaceutical compounds has been developed. Catalytic reactions are initiated by the action of Lewis acidic B(C₆F₅)₃ and D₂O, converting a drug molecule into the corresponding boron‐enolate. Ensuing deuteration of the enolate by in situ‐generated D₂O⁺−H then results in the formation of α‐deuterated bioactive carbonyl compounds with up to >98% deuterium incorporation.

Abstract

Methods for the regioselective ring‐opening of 3,4‐epoxy alcohols and 2,3‐epoxy alcohols with halide nucleophiles, using a diarylborinic acid catalyst, are disclosed. Ring‐opening occurs at the position proximal to the OH group, an effect ascribed to a catalytic tethering mechanism whereby coordination to the substrate OH group positions the diarylborinic acid to deliver a coordinated halide nucleophile. These methods provide access to halohydrin substitution patterns that were not previously accessible through catalytic epoxide ring‐opening reactions.

Synlett
DOI: 10.1055/s-0039-1690266

Six-membered cyclic amidines effectively catalyzed the reaction of carbon disulfide with epoxides under mild conditions, such as atmospheric pressure and ambient temperature, to give the corresponding cyclic dithiocarbonates (1,3-oxathiolane-2-thiones) in high yields.
[...]

© Georg Thieme Verlag Stuttgart · New York

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Aliphatic amines strongly coordinate, and therefore easily inhibit, the activity of transition-metal catalysts, posing a marked challenge to nitrogen-hydrogen (N–H) insertion reactions. Here, we report highly enantioselective carbene insertion into N–H bonds of aliphatic amines using two catalysts in tandem: an achiral copper complex and chiral amino-thiourea. Coordination by a homoscorpionate ligand protects the copper center that activates the carbene precursor. The chiral amino-thiourea catalyst then promotes enantioselective proton transfer to generate the stereocenter of the insertion product. This reaction couples a wide variety of diazo esters and amines to produce chiral α-alkyl α–amino acid derivatives.

Nature Catalysis, Published online: 18 November 2019; doi:10.1038/s41929-019-0378-4

In good shape: A manganese(I) complex containing a chiral (NH)₂P₂ macrocycle catalyzes the asymmetric transfer hydrogenation of a broad scope of ketones with the highest enantioselectivities obtained with this metal thus far. Noncovalent interactions between the incoming substrate and the macrocyclic ligand account for the excellent enantioselection.

Abstract

The bis(carbonyl) manganese(I) complex [Mn(CO)₂(1)]Br (2) with a chiral (NH)₂P₂ macrocyclic ligand (1) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2‐propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed.

Publication date: 27 December 2019

Source: Tetrahedron, Volume 75, Issue 52

Author(s): Naoto Aoyagi, Yoshio Furusho, Takeshi Endo

Graphical abstract